JP62-271982A published by the Japan Patent Office has disclosed a vane pump as mentioned below. The vane pump incorporates a cam ring into a body bore disposed in a body and also incorporates a rotor into the cam ring. A plurality of vanes is disposed inside the cam ring in such a way to freely move in the rotor and out of the rotor. The rotor is connected to a drive shaft and rotates with rotation of the drive shaft, as well as moves in and out the vanes disposed in the rotor along an inside face of the cam ring. In the process the rotor rotates, chambers defined by the neighboring vanes contract and expand. When the chamber expands, the vane pump is at the suction stroke, and when the chamber contracts, the vane pump is at the discharge stroke.
Further, a side plate is provided in one of side faces of the cam ring in a body side. The side plate has an outer diameter which is arranged to be equal to an outer diameter of the cam ring provided in the body bore. A discharge pressure or more of the pump is applied on the entire backside of the side plate to press the side plate on the side of the cam ring. This prevents a slight clearance between the cam ring and the side plate to widen due to pressures between the vanes, thus improving sealing properties of the chambers between the vanes.
In addition, a pair of locating pins are provided in a cover side of the vane pump in such a way to enter into a boundary portion between the cam ring and the body bore. Such arrangement determines a relative position relation between the body and the cover, as well as keeps the center of the body bore to be in line with the center of the cam ring and the side plate.